Web crawlers typically browse web documents in the World Wide Web at pre-determined time intervals, which may vary from several days to months. This time period may depend on the type or importance of a particular web document. Although an entire web index may be replaced each time it is crawled, the increment of time between crawl cycles may be too long to keep the web index current. For example, if certain information changes for a particular web document between crawl cycles, this information may not be reflected in search results, and as a result, a user may not be provided with current search results.